DOCSLIB.ORG

The T Tauri Star RY Tauri As a Case Study of the Inner Regions of Circumstellar Dust Disks

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The T Tauri Star RY Tauri As a Case Study of the Inner Regions of Circumstellar Dust Disks A&A 478, 779–793 (2008) Astronomy DOI: 10.1051/0004-6361:20077049 & c ESO 2008 Astrophysics The T Tauri star RY Tauri as a case study of the inner regions of circumstellar dust disks A. A. Schegerer1,S.Wolf1, Th. Ratzka2, and Ch. Leinert1 1 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: [email protected] 2 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany Received 3 January 2007 / Accepted 13 November 2007 ABSTRACT Aims. We study the inner region (∼1.0 AU up to a few 10 AUs) of the circumstellar disk around the “classical” T Tauri star RY Tau. Our aim is to find a physical description satisfying the available interferometric data, obtained with the mid-infrared interferometric instrument at the Very Large Telescope Interferometer, as well as the spectral energy distribution in the visible to millimeter wave- length range. We also compare the findings with the results of similar studies, including those of intermediate-mass Herbig Ae/Be stars. Methods. Our analysis is done within the framework of a passively heated circumstellar disk, which is optionally supplemented by the effects of accretion and an added envelope. To achieve a more consistent and realistic model, we used our continuum transfer code MC3D. In addition, we studied the shape of the 10 µm silicate emission feature in terms of the underlying dust population, both for single-dish and for interferometric measurements. Results. We show that a modestly flaring disk model with accretion can explain both the observed spectral energy distribution and the mid-infrared visibilities obtained with the mid-infrared infrared instrument. We found an interesting ambiguity: a circumstellar active disk model with an added envelope, and a lower accretion rate than in the active disk model without envelope, could represent the observations equally as well. This type of model with the envelope should be considered a viable alternative in future models of other T Tauri stars. The approach of a disk with a puffed-up inner rim wall and the influence of a stellar companion is also discussed. We also investigate the influence of various fit parameters on the outcome of the radiative transfer modeling. From the study of the silicate emission feature we see evidence for dust evolution in a T Tauri star, with a decreasing fraction of small amorphous and an increasing fraction of crystalline particles closer to the star. Key words. infrared: stars – accretion, accretion disks – astrochemistry – stars: planetary systems: protoplanetary disks – radiative transfer – instrumentation: interferometers 1. Introduction However, studies of the inner circumstellar regions (∼1AU)of objects in the closest star forming regions are only feasible by T Tauri stars are known as precursors of low-mass main se- < interferometric observations. quence stars (2–3 M). In contrast to main sequence stars, their Strong emission features in the MIR range at 10 µmand characteristic properties are strong emission line radiation (e.g., 20 µm corresponding to the Si-O stretching and bending modes Balmer α) and excessive continuum radiation observed in the of silicate grains, are assumed to result from absorption and ree- UV, infrared and the millimeter (mm) wavelength range of their mission processes in optically thin dust layers of the circum- spectral energy distribution (SED). It has been shown that the stellar disks. While silicate grains are expected to be initially spatial distribution of circumstellar dust in a disk or an enve- amorphous and small (<0.1 µm; Mathis et al. 1977, MRN there- lope that is primarily exposed to stellar radiation, is responsible after)1, the crystallization of amorphous silicates starts at tem- for the excess radiation in the infrared wavelength range (e.g., peratures of ∼1200 K (e.g., Gail 1998). Moreover, high dust Adams et al. 1987), while accretion of circumstellar material re- densities and turbulent processes in the interior of circumstel- sults in the UV excess and strong emission line radiation (see lar disks favor dust grain growth to dust pebbles (e.g., Blum Hartmann 1998, for a review). et al. 2000; Johansen et al. 2005). The shape of the emitted The extraordinary interest in the inner region of a circumstel- silicate feature allows the estimation of the predominant stage lar disk results from the assumption that the formation of planets of the dust evolution in a young stellar object (YSO). Different is favored there (see Nagasawa et al. 2006; Wünsch et al. 2005; degrees of crystallization and grain growth have already been Klahr 2004). While mm observations probe cooler outer disk re- shown in a large sample of T Tauri stars of different ages and gions and layers close to the midplane of circumstellar disks, stellar masses (e.g., Schegerer et al. 2006). As temperature and observations in the mid-infrared (MIR) wavelength regime are density increase in circumstellar disks with decreasing distance more sensitive to warmer (250 K < T < 1000 K; see Schegerer to the central star, crystallinity and grain size sensitively depend et al. 2006: Fig. 1) disk regions, such as the surface of the in- on the radial position of the dust in a circumstellar system (e.g., ner regions where dust is directly irradiated by the central star. Appendix A and Fig. A1 are only available in electronic form at 1 In this paper amorphous and small, i.e., primordial and interstellar http://www.aanda.org dust grains, are called not-evolved/undeveloped. Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20077049 780 A. A. Schegerer et al.: The inner regions of circumstellar dust disks Table 1. Observed properties of RY Tau. Parameter Value Reference RA (J2000.0) 04 21 57.41 DEC (J2000.0) +28 26 36 1 +54 Distance 134−31pc 2 Visual extinction (2.2 ± 0.2) mag 3 Spectral type F8 III 4 Stellar mass 1.69 M 5 Stellar luminosity 12.8 L 6 −8 Accretion rate 7.8 × 10 M/yr 3 Age (6.5 ± 0.9) Myr 7 References – 1: Perryman et al. (1997); 2: Bertout et al. (1999); 3: Calvet et al. (2004); 4: Mora et al. (2001); 5: Beckwith et al. (1990); 6: Akeson et al. (2005); 7: Siess et al. (1999). Fig. 1. The spectrally resolved, calibrated visibility data derived from ff our MIDI observations (Table 3). The error bars are the 1σ deviations Table 2. Photometric measurements of RY Tau. The data of di er- that result from the observations of different calibrators in one night. ent measurements are averaged and the standard deviation is deter- mined. For convience, all fluxes are given in Jansky and in magnitude. Conversion factors are taken from Leinert (1997). Beckwith et al. 1999; Weidenschilling 1997; Gail 2003: Fig. 28). Wavelength [µm] Flux [Jy] ([mag]) Reference In fact, observations with MID-infrared Interferometric instru- 0.36 (U)0.04 ± 0.01 (11.72 ± 0.16) 1 ment (MIDI) have already revealed a correlation between the ra- 0.45 (B)0.14 ± 0.01 (11.23 ± 0.08) 1 dial position and the evolutionary stage of silicate dust in circum- 0.55 (V)0.33 ± 0.01 (10.12 ± 0.04) 1 / stellar disks around Herbig Ae Be (HAeBe) stars, which are the 0.64 (RC)0.59 ± 0.03 (9.3 ± 0.05) 1 more massive counterparts of T Tauri stars (Leinert et al. 2004; 0.79 (IC)1.0 ± 0.06 (8.52 ± 0.06) 1 van Boekel et al. 2004). 1.25 (J)1.6 ± 0.8(7.64 ± 0.40) 2, 3 The density, temperature and compositional structure of cir- 1.65 (H)2.3 ± 0.9(6.48 ± 0.30) 2, 3 . ± . ± . cumstellar dust disks and surrounding envelopes have been the 2 20 (K)38 0 5(556 0 13) 2, 3 4.80 (M)6.6 ± 2.0(3.4 ± 0.28) 4, 5 central issue of many former studies (e.g., Chiang & Goldreich . ± . ff 11 0(N)200 0 36 1997; D’Alessio et al. 2001). Di erent modeling approaches 25 28 ± 37 have been tried to quantitatively explain and reproduce phe- 60 18 ± 47 nomenons like excess radiation, shapes of emission lines (e.g., 100 12 ± 57,8 Muzerolle et al. 2004; Natta et al. 2000), flux variations 1300 0.23 ± 0.02 9 (e.g., Herbig et al. 2003) and intensity distributions of images (e.g., Lucas et al. 1997). However, the evolution of (inner) disk References – 1: Calvet et al. (1997); 2: Gezari-Catalog (Gezari et al. 1999); 3: 2 MASS-Catalog (Cutri et al. 2003); 4: Rydgren et al. (1976); structure and its correlation to dust evolution is still unclear (e.g., 5: Elias (1978); 6: Hanner et al. (1998); 7: Strom et al. (1989); 8: Harvey Millan-Gabet et al. 2006; Beckwith et al. 1999), and has been un- et al. (1979); 9: Mora et al. (2001). derestimated in actual modeling approaches, or mainly reserved for theoretical studies (e.g., Gail 1998). However, interferomet- ric observations in the MIR wavelength range, which are now models of Akeson et al. (2005) where near-infared (NIR) vis- available, are sensitive to the inner disk structure where warm ibilites were modeled, and discuss discrepancies. Furthermore, dust dominates. Including their sensitivity for the silicate feature, we investigate the possibility of the existence of a stellar com- the correlation between inner disk structure and grain evolution panion and compare RY Tau with HAeBe stars. Section 8 sum- can be directly studied. marizes our results. In this paper we focus on modeling of the SED and spectrally resolved N band visibilities, which we obtained for the T Tauri 2.
Load more

Recommended publications
  • La Constellation Du Taureau
    La constellation du Taureau La constellation zodiacale du Taurus – le Taureau – est parfaitement visible sous les deux hémisphères d’avril à février. (1) Un peu de mythologie Selon la légende, l’œil rouge du puissant Taureau surveille Orion, le Chasseur, des avances duquel il veut protéger les Sept Sœurs – les Pléiades -. Le cœur d’Orion est tourné vers Mérope, l’une des sœurs dont il veut faire sa femme cependant qu’au bord de l’Amas des Pléiades, les parents de celle-ci le Titan Atlas et l’Océanide Pléioné – les observent attentivement. Des sept Pléiades, jeunes étoiles bleues saphir, seule Mérope a épousé un mortel, le roi de Corinthe, aussi cache-t-elle sa honte derrière une fine nébuleuse par réflexion. (2) (1) et (2) L’exploration du ciel, Robert Burnham, Alan Dyer, Robert A. Garfinkle, Martin George, Jeff Kanipi, David H. Levy. Édition Konemann, page 202. Chez les Babyloniens, le fermier (maintenant le Bélier) guide un Taureau qui manœuvre une charrue céleste creusant un sillon dans le ciel le long de l’écliptique. (3) Les Hyades sont les filles du dieu Atlas et de Pléione. Elles étaient 15 et avaient un frère nommé Hyas. Quand Hyas fut tué par un lion cinq des filles étaient inconsolables et ont été mises dans le ciel près de Hyas (constellation du Verseau) et ont été appelées les Hyades pour faire honneur à leur frère. Les sœurs qui restèrent pleuraient celles qui avaient été placées dans le ciel et à leur tour, s’y retrouvèrent et sont devenues les Pléiades. (4) (3) et (4) L’Observateur, revue électronique, http://astrosurf.com/duplessis/observateur/revue.html Volume 3, numéro 3, Constellation et ses étoiles, Rachelle Léger de la SAPM, page 2 Les Hyades (Mel 25) et les Pléiades (M 45) sont deux objets du ciel profond apparaissant dans le catalogue d’observation du CAABM.
    [Show full text]
  • Spectroscopic Analysis of Accretion/Ejection Signatures in the Herbig Ae/Be Stars HD 261941 and V590 Mon T Moura, S
    Spectroscopic analysis of accretion/ejection signatures in the Herbig Ae/Be stars HD 261941 and V590 Mon T Moura, S. Alencar, A. Sousa, E. Alecian, Y. Lebreton To cite this version: T Moura, S. Alencar, A. Sousa, E. Alecian, Y. Lebreton. Spectroscopic analysis of accretion/ejection signatures in the Herbig Ae/Be stars HD 261941 and V590 Mon. Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2020, 494 (3), pp.3512-3535. 10.1093/mnras/staa695. hal-02523038 HAL Id: hal-02523038 https://hal.archives-ouvertes.fr/hal-02523038 Submitted on 16 May 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. MNRAS 000,1–24 (2019) Preprint 27 February 2020 Compiled using MNRAS LATEX style file v3.0 Spectroscopic analysis of accretion/ejection signatures in the Herbig Ae/Be stars HD 261941 and V590 Mon T. Moura1?, S. H. P. Alencar1, A. P. Sousa1;2, E. Alecian2, Y. Lebreton3;4 1Universidade Federal de Minas Gerais, Departamento de Física, Av. Antônio Carlos 6627, 31270-901, Brazil 2Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France 3LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ.
    [Show full text]
  • THE STAR FORMATION NEWSLETTER an Electronic Publication Dedicated to Early Stellar Evolution and Molecular Clouds
    THE STAR FORMATION NEWSLETTER An electronic publication dedicated to early stellar evolution and molecular clouds No. 90 — 27 March 2000 Editor: Bo Reipurth ([email protected]) Abstracts of recently accepted papers The Formation and Fragmentation of Primordial Molecular Clouds Tom Abel1, Greg L. Bryan2 and Michael L. Norman3,4 1 Harvard Smithsonian Center for Astrophysics, MA, 02138 Cambridge, USA 2 Massachusetts Institute of Technology, MA, 02139 Cambridge, USA 3 LCA, NCSA, University of Illinois, 61801 Urbana/Champaign, USA 4 Astronomy Department, University of Illinois, Urbana/Champaign, USA E-mail contact: [email protected] Many questions in physical cosmology regarding the thermal history of the intergalactic medium, chemical enrichment, reionization, etc. are thought to be intimately related to the nature and evolution of pregalactic structure. In particular the efficiency of primordial star formation and the primordial IMF are of special interest. We present results from high resolution three–dimensional adaptive mesh refinement simulations that follow the collapse of primordial molecular clouds and their subsequent fragmentation within a cosmologically representative volume. Comoving scales from 128 kpc down to 1 pc are followed accurately. Dark matter dynamics, hydrodynamics and all relevant chemical and radiative processes (cooling) are followed self-consistently for a cluster normalized CDM structure formation model. Primordial molecular clouds with ∼ 105 solar masses are assembled by mergers of multiple objects that have formed −4 hydrogen molecules in the gas phase with a fractional abundance of ∼< 10 . As the subclumps merge cooling lowers the temperature to ∼ 200 K in a “cold pocket” at the center of the halo. Within this cold pocket, a quasi–hydrostatically > 5 −3 contracting core with mass ∼ 200M and number densities ∼ 10 cm is found.
    [Show full text]
  • XIII Publications, Presentations
    XIII Publications, Presentations 1. Refereed Publications E., Kawamura, A., Nguyen Luong, Q., Sanhueza, P., Kurono, Y.: 2015, The 2014 ALMA Long Baseline Campaign: First Results from Aasi, J., et al. including Fujimoto, M.-K., Hayama, K., Kawamura, High Angular Resolution Observations toward the HL Tau Region, S., Mori, T., Nishida, E., Nishizawa, A.: 2015, Characterization of ApJ, 808, L3. the LIGO detectors during their sixth science run, Classical Quantum ALMA Partnership, et al. including Asaki, Y., Hirota, A., Nakanishi, Gravity, 32, 115012. K., Espada, D., Kameno, S., Sawada, T., Takahashi, S., Ao, Y., Abbott, B. P., et al. including Flaminio, R., LIGO Scientific Hatsukade, B., Matsuda, Y., Iono, D., Kurono, Y.: 2015, The 2014 Collaboration, Virgo Collaboration: 2016, Astrophysical Implications ALMA Long Baseline Campaign: Observations of the Strongly of the Binary Black Hole Merger GW150914, ApJ, 818, L22. Lensed Submillimeter Galaxy HATLAS J090311.6+003906 at z = Abbott, B. P., et al. including Flaminio, R., LIGO Scientific 3.042, ApJ, 808, L4. Collaboration, Virgo Collaboration: 2016, Observation of ALMA Partnership, et al. including Asaki, Y., Hirota, A., Nakanishi, Gravitational Waves from a Binary Black Hole Merger, Phys. Rev. K., Espada, D., Kameno, S., Sawada, T., Takahashi, S., Kurono, Lett., 116, 061102. Y., Tatematsu, K.: 2015, The 2014 ALMA Long Baseline Campaign: Abbott, B. P., et al. including Flaminio, R., LIGO Scientific Observations of Asteroid 3 Juno at 60 Kilometer Resolution, ApJ, Collaboration, Virgo Collaboration: 2016, GW150914: Implications 808, L2. for the Stochastic Gravitational-Wave Background from Binary Black Alonso-Herrero, A., et al. including Imanishi, M.: 2016, A mid-infrared Holes, Phys.
    [Show full text]
  • New Herbig±Haro Objects and Giant Outflows in Orion
    Mon. Not. R. Astron. Soc. 310, 331±354 (1999) New Herbig±Haro objects and giant outflows in Orion S. L. Mader,1 W. J. Zealey,1 Q. A. Parker2 and M. R. W. Masheder3,4 1Department of Engineering Physics, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia 2Anglo-Australian Observatory, Coonabarabran, NSW 2357, Australia 3Department of Physics, University of Bristol, Bristol BS8 1TL 4Netherlands Foundation for Research in Astronomy, PO Box 2, 7990 AA Dwingeloo, the Netherlands Accepted 1999 June 29. Received 1999 May 11; in original form 1998 June 25 ABSTRACT We present the results of a photographic and CCD imaging survey for Herbig±Haro (HH) objects in the L1630 and L1641 giant molecular clouds in Orion. The new HH flows were initially identified from a deep Ha film from the recently commissioned AAO/UKST Ha Survey of the southern sky. Our scanned Ha and broad-band R images highlight both the improved resolution of the Ha survey and the excellent contrast of the Ha flux with respect to the broad-band R. Comparative IVN survey images allow us to distinguish between emission and reflection nebulosity. Our CCD Ha,[Sii], continuum and I-band images confirm the presence of a parsec-scale HH flow associated with the Ori I-2 cometary globule, and several parsec-scale strings of HH emission centred on the L1641-N infrared cluster. Several smaller outflows display one-sided jets. Our results indicate that, for declinations south of 268 in L1641, parsec-scale flows appear to be the major force in the large-scale movement of optical dust and molecular gas.
    [Show full text]
  • Observations of T-Tauri Stars Using HST-GHRS: II. Optical and Near UV Lines David R
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server Submitted to ApJ Observations of T-Tauri Stars using HST-GHRS: II. Optical and Near UV lines David R. Ardila1, Gibor Basri2, Frederick M. Walter3, Jeff A. Valenti4, Christopher M. Johns-Krull5 ABSTRACT We have analyzed GHRS data of eight Classical T Tauri stars (CTTSs) and one Weak T Tauri star (WTTS). The GHRS data consist of an spectral range 40 A˚ wide centered on 2800 A.˚ For 4 of the CTTS we have nearly simultaneous optical observations which contain Hα,Hβ,HeI,NaD,andtheCaII infrared triplet. The Mg II resonance doublet is the strongest feature in the 2800 A˚ range. This line has a fairly wide and symmetric emission component ( 200 1 ∼ to 300 km s− for the CTTSs), with a narrow central absorption and a wide ∼ blueshifted absorption superimposed to it. The narrow central absorption width and equivalent width are inconsistent with being due only to ISM clouds described in the literature, which lead us to conclude that it is partially due to non-LTE processes in the emission line region itself. The emission profile closely follows Hα. Its large width in CTTS cannot be due to the Stark effect and we suggest that it is due to supersonic turbulence. All the stars show blueshifted absorptions 1 that are evidence of outflows (terminal velocities 300 km s− ), with multiple ∼ flows observed in two stars. We show evidence that the wind is not spherical, with wind signatures being stronger for lower inclinations at a given accretion rate.
    [Show full text]
  • A Hipparcos Study of the Hyades Open Cluster
    A&A 367, 111–147 (2001) Astronomy DOI: 10.1051/0004-6361:20000410 & c ESO 2001 Astrophysics A Hipparcos study of the Hyades open cluster Improved colour-absolute magnitude and Hertzsprung{Russell diagrams J. H. J. de Bruijne, R. Hoogerwerf, and P. T. de Zeeuw Sterrewacht Leiden, Postbus 9513, 2300 RA Leiden, The Netherlands Received 13 June 2000 / Accepted 24 November 2000 Abstract. Hipparcos parallaxes fix distances to individual stars in the Hyades cluster with an accuracy of ∼6per- cent. We use the Hipparcos proper motions, which have a larger relative precision than the trigonometric paral- laxes, to derive ∼3 times more precise distance estimates, by assuming that all members share the same space motion. An investigation of the available kinematic data confirms that the Hyades velocity field does not contain significant structure in the form of rotation and/or shear, but is fully consistent with a common space motion plus a (one-dimensional) internal velocity dispersion of ∼0.30 km s−1. The improved parallaxes as a set are statistically consistent with the Hipparcos parallaxes. The maximum expected systematic error in the proper motion-based parallaxes for stars in the outer regions of the cluster (i.e., beyond ∼2 tidal radii ∼20 pc) is ∼<0.30 mas. The new parallaxes confirm that the Hipparcos measurements are correlated on small angular scales, consistent with the limits specified in the Hipparcos Catalogue, though with significantly smaller “amplitudes” than claimed by Narayanan & Gould. We use the Tycho–2 long time-baseline astrometric catalogue to derive a set of independent proper motion-based parallaxes for the Hipparcos members.
    [Show full text]
  • Multicolor Photometric Behavior of the Young Stellar Object V1704 Cygni
    Multicolor photometric behavior of the young stellar object V1704 Cygni Sunay Ibryamov1, Evgeni Semkov2, Stoyanka Peneva2, U˘gur Karadeniz3 1 Department of Physics and Astronomy, University of Shumen, 115, Universitetska Str., 9700 Shumen, Bulgaria 2 Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, 72, Tsarigradsko Shose Blvd., 1784 Sofia, Bulgaria 3 Department of Physics, Izmir Institute of Technology, Urla, 35430 Izmir, Turkey [email protected] (Submitted on 22.01.2018. Accepted on 20.02.2018) Abstract. Results from BV RI photometric observations of the pre-main sequence star V1704 Cyg collected during the time period from August 2010 to December 2017 are presented. The star is located in the star-forming HII region IC 5070 and it exhibits photometric variability in all optical passbands. After analyzing the obtained data, V1704 Cyg is classified as a classical T Tauri star. Key words: stars: pre-main sequence, stars: variables: T Tauri, star: individual: (V1704 Cyg) 1. Introduction One of the most frequent types of pre-main sequence (PMS) stars are the low-mass (M ≤ 2M⊙) T Tauri stars (TTSs). The first study of the TTSs as a separate class of variables with the prototype star T Tau was made by Joy (1945). These stars show irregular photometric variability and emission spectra. TTSs are divided into two sub-classes: classical T Tauri stars (CTTSs) still actively accreting from their massive circumstellar disks and the weak- line T Tauri stars (WTTSs) without evidence of disk accretion (M´enard
    [Show full text]
  • Radio Constraints on Activity in Young Brown Dwarfs
    in prep. Radio Constraints on Activity in Young Brown Dwarfs Rachel A. Osten1 Department of Astronomy, University of Maryland, College Park, MD 20742-2421, U.S.A. Electronic Mail: [email protected] Ray Jayawardhana Department of Astronomy & Astrophysics, University of Toronto, Toronto, ON M5S 3H8, CANADA Electronic Mail: [email protected] ABSTRACT We report on searches for radio emission from three of the nearest known young brown dwarfs using the Very Large Array. We have obtained sensitive upper limits on 3.6cm emission from 2MASSW J1207334-393254, TWA 5B and SSSPM J1102-3431, all of which are likely members of the ∼8-Myr-old TW Hy- drae association. We derive constraints on the magnetic field strength and the number density of accelerated electrons, under the assumption that young brown dwarf atmospheres are able to produce gyrosynchrotron emission, as seems to be indicated in older brown dwarfs. For the young brown dwarf TWA 5B, the ratio of its detected X-ray luminosity to the upper limit on radio luminosity places arXiv:astro-ph/0604521v2 27 Apr 2006 it within the expected range for young stars and older, active stars. Thus, its behavior is anomalous compared to older brown dwarfs, in which radio luminos- ity is substantially enhanced over the expected relationship. Our observations deepen the conundrum of magnetic activity in brown dwarfs, and suggest that a factor other than age is more important for determining radio emission in cool substellar objects. Subject headings: stars: activity – stars: coronae – stars: low mass, brown dwarfs – stars: pre-main-sequence – radio continuum 1Hubble Fellow –2– 1.
    [Show full text]
  • Des Projets D'envergure Astro Débutant Ciel Profond
    Une publication de la Société d’astronomie du Planétarium de Montréal • SAPM Hiver 2014-2015 — volume 25, numéro 4 Le ciel des Hommes par Gilbert St-Onge - p.4 Des projets d’envergure par Gilbert St-Onge - p.8 Astro débutant par Charles Gagné - p.10 Ciel profond par Suzanne Parent - p.14 Photos : Sarah Cartwright, Gilbert Cartwright, : Sarah Photos et HST St-Onge CONVENTION DE LA POSTE-PUBLICATIONS No 41017003 Retourner toute correspondance ne pouvant être livrée Mot du Président - Malgré le froid, profitez du ciel de l’hiver au Canada au Service des publications 123, rue Sainte-Catherine, Montréal, QC, H3Z 2Y7 Courriel : [email protected] Les belles soirées d’astronomie d’hiver sont à nos Société d’astronomie du Planétarium de Montréal portes. Nous pourrons profiter d’une durée de la nuit plus 4801, av. Pierre-de Coubertin, Montréal (QC) H1V 3V4 www.sapm.qc.ca longue et de ciels généralement plus cristallins, mais il faudra Facebook : facebook.com/ s’habiller chaudement. Societedastronomieduplanetariumdemontreal Twitter : twitter.com/sapm_astro La technique de l’oignon est la meilleure méthode pour pou- La Société d’astronomie du Planétarium de Montréal voir rester au chaud. Portez d’abord d’une première couche de (SAPM) est un organisme à but non lucratif dont les sous-vêtements chauds. Ajoutez ensuite une seconde plus épaisse principaux objectifs sont de promouvoir l’astronomie auprès du grand public en organisant des événements de type fibre polaire pour retenir la chaleur et terminez par une spéciaux lors de différents phénomènes astronomiques couche très chaude qui retiendra la chaleur et coupera le vent (pluies d’étoiles filantes, éclipses, comètes brillantes, etc.), de favoriser les échanges entre les astronomes amateurs glacial d’hiver.
    [Show full text]
  • Information Bulletin on Variable Stars
    COMMISSIONS AND OF THE I A U INFORMATION BULLETIN ON VARIABLE STARS Nos November July EDITORS L SZABADOS K OLAH TECHNICAL EDITOR A HOLL TYPESETTING K ORI ADMINISTRATION Zs KOVARI EDITORIAL BOARD L A BALONA M BREGER E BUDDING M deGROOT E GUINAN D S HALL P HARMANEC M JERZYKIEWICZ K C LEUNG M RODONO N N SAMUS J SMAK C STERKEN Chair H BUDAPEST XI I Box HUNGARY URL httpwwwkonkolyhuIBVSIBVShtml HU ISSN COPYRIGHT NOTICE IBVS is published on b ehalf of the th and nd Commissions of the IAU by the Konkoly Observatory Budap est Hungary Individual issues could b e downloaded for scientic and educational purp oses free of charge Bibliographic information of the recent issues could b e entered to indexing sys tems No IBVS issues may b e stored in a public retrieval system in any form or by any means electronic or otherwise without the prior written p ermission of the publishers Prior written p ermission of the publishers is required for entering IBVS issues to an electronic indexing or bibliographic system to o CONTENTS C STERKEN A JONES B VOS I ZEGELAAR AM van GENDEREN M de GROOT On the Cyclicity of the S Dor Phases in AG Carinae ::::::::::::::::::::::::::::::::::::::::::::::::::: : J BOROVICKA L SAROUNOVA The Period and Lightcurve of NSV ::::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::: W LILLER AF JONES A New Very Long Period Variable Star in Norma ::::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::::: EA KARITSKAYA VP GORANSKIJ Unusual Fading of V Cygni Cyg X in Early November :::::::::::::::::::::::::::::::::::::::
    [Show full text]
  • Young Stellar Object Candidates Toward the Orion Region Selected from GALEX (Research Note)
    A&A 572, A89 (2014) Astronomy DOI: 10.1051/0004-6361/201424629 & c ESO 2014 Astrophysics Young stellar object candidates toward the Orion region selected from GALEX (Research Note) Nestor Sanchez, Ana Inés Gómez de Castro, Fátima Lopez-Martinez, and Javier López-Santiago S. D. Astronomía y Geodesia, Fac. CC. Matemáticas, Universidad Complutense de Madrid, 28040 Madrid, Spain e-mail: [email protected] Received 18 July 2014 / Accepted 28 October 2014 ABSTRACT We analyze 359 ultraviolet tiles from the All Sky Imaging Survey of the space mission GALEX covering roughly 400 square degrees toward the Orion star-forming region. There are a total of 1 555 174 ultraviolet sources that were cross-matched with other catalogs (2MASS, UCAC4, SDSS, DENIS, CMC15, and WISE) to produce a list of 290 717 reliable sources with a wide range of photometric information. Using different color selection criteria, we identify 111 young stellar object candidates showing both ultraviolet and infrared excesses, of which 81 are new identifications. We discuss the spatial distribution, the spectral energy distributions, and other physical properties of these stars. Their properties are, in general, compatible with those expected for T Tauri stars. This population of TTS candidates is widely dispersed around the Orion molecular cloud. Key words. stars: low-mass – stars: pre-main sequence – stars: variables: T Tauri, Herbig Ae/Be – ultraviolet: stars 1. Introduction and magnetic stellar activity (Edwards et al. 1994; Muzerolle et al. 1998). As spectroscopic observations are time consuming The current paradigm for low-mass star formation catego- and are sometimes restricted to bright objects, a good strategy is rizes young stellar objects (YSOs) into four general classes: to perform spectroscopic follow-ups only for the most reliable Class 0 sources are faint central protostars surrounded by a YSO candidates selected using photometric methods.
    [Show full text]